Sorry if this question is too stupid, but I wonder what would happen if a passenger on the first row just behind the cockpit (ie. on a 737) starts screaming "GO AROUND" when the plane is about to touch down. Can it confuse the pilots?
Not likely. Pilots wear headphones, so we cannot hear the idle prattle of the pax in the hold. In any case, we don't take orders from passengers. Think about that for a second: would you like it if aircraft pilots followed the instructions of a crazy screaming passenger? What if there were TWO crazy screaming passengers giving contradictory commands? Which one should we obey?
In any case, nowadays cockpit doors are closed during flight anyway.
Unless he’s shouting “cow on the runway”, I don’t even hear my copilot on finals as he mutters “too fast/slow”, “too high/low”, “left a bit”, etc., but I hear fine as we taxi and he says “Coffee’s on me”.
No, but the passenger is likely to be arrested for causing such a disruption and face serious charges. The authorities don't react kindly to that kind of crap in a post 9/11 world.
The chosen answer is correct so far, no doubt. But in my eyes, it lacks some generality and an important point:
While it is certainly true for a 737 that a pilot won't hear you and therefore take no action, I'd add that is can be true for smaller aircrafts when you hear the passenger as they may even can speak over the intercom (say a Cessna 172). As a pilot, you have to decide, if you realize that it was a passenger screaming "go around", if you take action. You train a lot of things as a pilot, one of the most important one is to make a go around as fast as possible if anyone screams it (normally co-pilot, flight student etc) and you do not think about whether it is right or not (you assume he had a good reason) because there is no time, you better focus on the maneuver.
The conclusion is nearly the same as mentioned in other answers with the small addition that, if the pilot hears you, you may trigger it's trained reflexes and he will make a go-around.
If there is a legitimate need for a go-around like an emergency that the pilots can't see but the passenger can or landing at the wrong airport, then it might influence the pilots. However, that might not happen because of the conditions described by @Tyler Durden's answer.